The field of the disclosure relates generally to wind turbines, and more particularly to a system and method for controlling wind turbines to reduce load imbalances under certain operating conditions, e.g., blade-pitch failure.
Many known wind turbines are used to generate power by harnessing wind energy present in the environment. During operation, such wind turbines may experience various fault conditions. Some of the fault conditions may be rectified while the wind turbine is in operation and some of the fault conditions may require the wind turbine to shut down. Once a shutdown command is generated by a wind turbine controller, the wind turbine initiates a standard process to shut down the wind turbine. During the standard process of shutting down the wind turbine, undesirable loads are induced in some of the wind turbine components that lead to accelerated wear and a possible shortening of the service life of such components. Specifically, the process of shutdown leads to high mechanical loads in wind turbine components such as a hub, a tower and a foundation of the wind turbine.
Furthermore, failure of a blade pitch system in the wind turbine or a deviation of a blade pitch angle from a determined set point during the process of shutdown may amplify the undesirable loads in the wind turbine. Currently, various approaches have been employed to address the issue of undesirable loads generated in the wind turbine. One such approach is to use mechanical brakes positioned on a generator shaft to shut down the wind turbine. However, using mechanical brakes leads to higher maintenance costs due to the accelerated wear of the mechanical brake components.
Another conventional approach is to use an open loop control technique to shut down the wind turbine that includes pitching out the wind turbine blades from an operating position to a feathered parking position using a fixed, pre-defined pitch-out profile. Unfortunately, this technique entails specific manual tuning and optimization of control parameters for each unique wind turbine configuration. Moreover, a single pitch-out profile is employed to control the wind turbine blades at different initial pitch angles and varying wind conditions during the shutdown, thereby resulting in inefficiencies and a suboptimal performance of the wind turbine.